1. Field of the Invention
The present invention relates to a device control device, a device control method, and a computer program. More specifically, the present invention relates to a device control device, a device control method, and a computer program that control an operation unique to another device by using a digital interface for transmitting signals.
2. Description of the Related Art
A high-definition multimedia interface (HDMI) has been widespread as a digital interface for transmitting video (image) signals and audio signals. The HDMI is based on a digital visual interface (DVI) standard, which is a standard for connection between a personal computer (PC) and a display, and is arranged for audio visual (AV) devices by adding an audio transmission function and a copyright protection function. High-Definition Multimedia Interface Specification Version 1.4 describes the details of the HDMI standard.
The interface based on the HDMI standard is capable of performing bidirectional transmission of a control signal, and is thus capable of transmitting a control signal from a television receiver to an output device, such as a set top box (STB) or a video disc player, connected via an HDMI cable. With such transmission of a control signal from a television receiver, a user can operate an entire AV system using a remote control of the television receiver. Examples of the signal transmitted through a transmission cable of the HDMI standard include a control instruction for controlling a device, a response to the instruction, and a signal representing a status of a device. In this specification, those signals are collectively referred to as control signals.
In the HDMI standard, interdevice control using consumer electronics control (CEC) is defined. The CEC is a single transmission line provided in the HDMI standard and performs bidirectional data transmission. By using the CEC line, various controls can be performed on the basis of unique physical addresses and logical addresses assigned to individual devices existing on an HDMI network. For example, if a video disc player connected to a television receiver via an HDMI cable is operated while a user is watching and listening to digital broadcast on the television receiver, the television receiver automatically switches the input to that of the video disc player. Also, a menu displayed by the video disc player and on/off of the power can be operated from a remote control of the television receiver.
According to the HDMI standard, a maximum of ten devices, including a television receiver, can be connected. Thus, a maximum of nine external devices can be connected to one television receiver. If the number of external devices connected to the television receiver is nine, any of the devices can be operated from a remote control.
In the HDMI standard, “Active Source” is defined as a CEC message for indicating a device that is displaying an image in the television receiver. According to this definition, for example, when a user operates a play button of a video disc player compatible with the HDMI standard, the video disc player outputs an AV stream if the video disc player is in a status capable of outputting a stable video signal (that is, in an active status). Also, the video disc player broadcasts an “Active Source” message indicating that the video disc player is an active device.
Here, “broadcast” means simultaneous transmission of a signal to all devices, not to a specific device. The television receiver and the other external devices that have received the “Active Source” message switch paths in order to play back the AV stream output from the video disc player.
As described above, in the HDMI standard, it is defined that the device that starts displaying video in the television receiver broadcasts an “Active Source” message to the other devices in the network. Note that the “Active Source” message is one of CEC messages defined in the HDMI standard.
Also, as described in Japanese Unexamined Patent Application Publication No. 2008-35399, for example, a function of changing a playback sound field in accordance with genre information of an electronic program guide (EPG) as electronic program information obtained in the television receiver has been realized as the control based on HDMI-CEC. In this function, genre information of the EPG is output to an HDMI-CEC line at the start of receiving a program that is watched/listened to in the television receiver or at the change of a program. The genre information provided through the CEC line is received by an audio playback device, such as an AV amplifier, whereby a playback sound field is set in accordance with the genre information.
For example, when a user wants to watch/listen to a sport program, the user can set a playback mode for obtaining a realistic sensation of the sport program. When a user wants to watch/listen to a news program, the user can set a playback mode for easily listening to sound (speech).